43,876 research outputs found
BRST quantization of the massless minimally coupled scalar field in de Sitter space (zero modes, euclideanization and quantization)
We consider the massless scalar field on the four-dimensional sphere .
Its classical action is degenerate
under the global invariance . We then quantize
the massless scalar field as a gauge theory by constructing a BRST-invariant
quantum action. The corresponding gauge-breaking term is a non-local one of the
form where
is a gauge parameter and is the volume of . It allows us to
correctly treat the zero mode problem. The quantum theory is invariant under
SO(5), the symmetry group of , and the associated two-point functions have
no infrared divergence. The well-known infrared divergence which appears by
taking the massless limit of the massive scalar field propagator is therefore a
gauge artifact. By contrast, the massless scalar field theory on de Sitter
space - the lorentzian version of - is not invariant under the
symmetry group of that spacetime SO(1,4). Here, the infrared divergence is
real. Therefore, the massless scalar quantum field theories on and
cannot be linked by analytic continuation. In this case, because of zero modes,
the euclidean approach to quantum field theory does not work. Similar
considerations also apply to massive scalar field theories for exceptional
values of the mass parameter (corresponding to the discrete series of the de
Sitter group).Comment: This paper has been published under the title "Zero modes,
euclideanization and quantization" [Phys. Rev. D46, 2553 (1992)
Analytic Results for the Gravitational Radiation from a Class of Cosmic String Loops
Cosmic string loops are defined by a pair of periodic functions and
, which trace out unit-length closed curves in three-dimensional
space. We consider a particular class of loops, for which lies along
a line and lies in the plane orthogonal to that line. For this class
of cosmic string loops one may give a simple analytic expression for the power
radiated in gravitational waves. We evaluate exactly in
closed form for several special cases: (1) a circle traversed
times; (2) a regular polygon with sides and interior vertex angle
; (3) an isosceles triangle with semi-angle .
We prove that case (1) with is the absolute minimum of within
our special class of loops, and identify all the stationary points of
in this class.Comment: 15 pages, RevTex 3.0, 7 figures available via anonymous ftp from
directory pub/pcasper at alpha1.csd.uwm.edu, WISC-MILW-94-TH-1
High resolution imaging of the Venus night side using a Rockwell 128x128 HgCdTe array
The University of Hawaii operates an infrared camera with a 128x128 HgCdTe detector array on loan from JPL's High Resolution Imaging Spectrometer (HIRIS) project. The characteristics of this camera system are discussed. The infrared camera was used to obtain images of the night side of Venus prior to and after inferior conjunction in 1988. The images confirm Allen and Crawford's (1984) discovery of bright features on the dark hemisphere of Venus visible in the H and K bands. Our images of these features are the best obtained to date. Researchers derive a pseudo rotation period of 6.5 days for these features and 1.74 microns brightness temperatures between 425 K and 480 K. The features are produced by nonuniform absorption in the middle cloud layer (47 to 57 Km altitude) of thermal radiation from the lower Venus atmosphere (20 to 30 Km altitude). A more detailed analysis of the data is in progress
Origin of Superconductivity in Boron-doped Diamond
Superconductivity of boron-doped diamond, reported recently at T_c=4 K, is
investigated exploiting its electronic and vibrational analogies to MgB2. The
deformation potential of the hole states arising from the C-C bond stretch mode
is 60% larger than the corresponding quantity in MgB2 that drives its high Tc,
leading to very large electron-phonon matrix elements. The calculated coupling
strength \lambda ~ 0.5 leads to T_c in the 5-10 K range and makes phonon
coupling the likely mechanism. Higher doping should increase T_c somewhat, but
effects of three dimensionality primarily on the density of states keep doped
diamond from having a T_c closer to that of MgB2.Comment: Four pages with two embedded figures, corrected fig1. (To appear in
Physical Review Letters(2004)
Gas perturbations in cool cores of galaxy clusters: effective equation of state, velocity power spectra and turbulent heating
We present the statistical analysis of X-ray surface brightness and gas
density fluctuations in cool cores of ten, nearby and bright galaxy clusters
that have deep Chandra observations and show observational indications of
radio-mechanical AGN feedback. Within the central parts of cool cores the total
variance of fluctuations is dominated by isobaric and/or isothermal
fluctuations on spatial scales ~ 10-60 kpc, which are likely associated with
slow gas motions and bubbles of relativistic plasma. Adiabatic fluctuations
associated with weak shocks constitute less than 10 per cent of the total
variance in all clusters. The typical amplitude of density fluctuations is
small, ~ 10 per cent or less on scales of ~ 10-15 kpc. Subdominant contribution
of adiabatic fluctuations and small amplitude of density fluctuations support a
model of gentle AGN feedback as opposed to periodically explosive scenarios
which are implemented in some numerical simulations. Measured one-component
velocities of gas motions are typically below 100-150 km/s on scales < 50 kpc,
and can be up to ~ 300 km/s on ~ 100 kpc scales. The non-thermal energy is < 12
per cent of the thermal energy. Regardless of the source that drives these
motions the dissipation of the energy in such motions provides heat that is
sufficient to balance radiative cooling on average, albeit the uncertainties
are large. Presented results here support previous conclusions based on the
analysis of the Virgo and Perseus Clusters, and agree with the Hitomi
measurements. With next generation observatories like Athena and Lynx, these
techniques will be yet more powerful.Comment: 16 pages, 11 figures, submitted to MNRA
Ab initio mass tensor molecular dynamics
Mass tensor molecular dynamics was first introduced by Bennett [J. Comput.
Phys. 19, 267 (1975)] for efficient sampling of phase space through the use of
generalized atomic masses. Here, we show how to apply this method to ab initio
molecular dynamics simulations with minimal computational overhead. Test
calculations on liquid water show a threefold reduction in computational effort
without making the fixed geometry approximation. We also present a simple
recipe for estimating the optimal atomic masses using only the first
derivatives of the potential energy.Comment: 19 pages, 5 figure
Epstein\u27s Challenge to the Civil Rights Regime
This Article takes a close look at the government\u27s determination of the substantive meaning of nondiscrimination in order to better evaluate the relation between the current practice of the civil rights regime and the alternative suggested by Richard Epstein in his book Forbidden Grounds: The Case Against Employment Discrimination Laws. It also analyzes the limit condition view of government, namely that the government may in no way discriminate, and everyone cannot be prevented from discriminating. The author concludes that defenders of the civil rights regime must engage Epstein\u27s argument, because failing to do so will be to fail either to defend or transcend the civil rights regime
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